New Pb-free materials require thorough characterization of mechanical properties because they are different from SnPb, and they can have different properties in various conditions too. There are few possibilities to investigate mechanical properties of solder materials. To assess reliability and damage to the solder joint, a range of methods can be employed. There can be either destructive or non-destructive assessments. The non-destructive approach is to use continuity testing, and by analyzing the response from a large number of joints with either lognormal or Weibull distributions, a failure prediction can be made. The destructive methods do not require a complete failure for the damage level to be assessed, thus fewer thermal cycles are required. Two techniques commonly used are dye penetration and shear measurement. Dye penetration measures the fatigue in terms of a crack area and shear measurement gives maximum strength i.e. the force required to break the solder joint. For shear stress, testing chip resistors were chosen as follows: 1206, 0805 and 0603. Boards with assembled resistors were thermally cycled for 1200 cycles in 6 different thermal profiles before the shear testing. The thermal cycles include dry air, liquid-liquid and HAST thermal profiles. Results from shear tests to assess the relative damage caused by a range of thermal cycle regimes are presented for Sn/3.5Ag and Sn/3.8Ag/0.7Cu solders. Shear testing was established as destructive method for evaluating the degree of crack propagation and damage to the solder joint as well as general strength of solder joint can be determined with that way.
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